The environmental concerns and the European liquid (bio) fuel regulations have determined a growing demand on biofuels. Fischer–Tropsch synthesis can provide clean synthetic fuels containing low concentrations of sulfur, nitrogen, and aromatics. While Fischer–Tropsch synthesis using natural gas and coal is a well established and commercialized process for more than 70 years, the new technology of Fischer–Tropsch synthesis using biomass as feedstock is gaining more and more attention due to the possibilities of using renewable raw materials. In this work, in order to optimize the Fischer–Tropsch synthesis, the influence of operating conditions has been studied in a slurry reactor using a Co-based catalyst. Experiments were performed at different syngas composition (variation of H2/CO ratio) and pressure (24, 20, and 16 bar), keeping the other parameters (temperature, 230 °C; gas flow, 5 Nm3/h) constant. The effects of pressure on CO conversion, product distribution, C 5+ selectivity, Par/Ole ratio, and α value were investigated, and the results were compared with data from literature. It was found that—increasing the reaction pressur ... mehre—heavier hydrocarbons were formed, and CO conversion increased from 44.2 to 63.7 %. A slight change has been observed in the case of an α value between 0.89 and 0.9, C 5+ selectivity between 90.6 and 91.7 %, and Par/Ole ratio between 11.4 and 14.1. An important role for the results obtained was attributed to H2/CO ratio variation during the experiments.